"Peptides containing 1,2,3,4-tetrahydroquinoline-2-carboxylic acids" are described by G. P. Zecchini et al in J. Heterocyclic Chem. 16, 1589 (1979), for the cyclization with acetic anhydride, to form "1H,3H,5H-oxazolo[3,4-a]quinolin-3-one derivatives". Also, 1-(mercapto- or acylthioalkanoyl)-1,2,3,4-tetrahydroquinoline-2-carboxylic acids, and salts thereof, are known, e.g., according to DOS No. 3,004,370, as possessing antihypertensive activity. Surprisingly it was found that by exchange of either the former mono-peptide, or the latter mercaptoalkanoyl moiety, by a carboxy-alkanoyl or aralkanoyl moiety, superior antihypertensive agents are obtained.